Isolation Throws are a front leg stabilization drill.
The athlete starts by balancing on their lead leg, the leg they land on when pitching.
They then coil the upper body so the shoulders now face perpendicular to the target.
As they coil, the back knee comes forward to assist with balance.
Finally they will uncoil the body, kick the back foot rearwards and deliver the ball.
The goal is to feel the front leg being strong and grounded on each throw. If you can deliver the ball without falling over, you have achieved front leg stability.